1. Field of the Invention
The present invention relates to determining the relationship between the jaws of a patient and particularly to occlusion analysis. More specifically, this invention is directed to apparatus which may be employed for occlusion analysis and especially to such apparatus wherein maxillary and mandibular models derived from a patient may be supported and manipulated relative to one another in order to permit an analysis of malocclusions. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
It is well known that the functioning of the stomatic system is affected by the teeth, jaw joints, muscles and nerves. It is further known that the spatial position of the mandible and condyles is determined by the cooperating rows of teeth when in the central occlusion position. Functional impairments in the muscle and mandibular joint area are caused by mandibular displacements. Restated, if such a displacement results in the relationship between maxilla and mandible being such that the condyles are not in a balanced, compression-free state in their hinge position, the greatest possible inactivation of the muscle groups exists. This is a condition which may require treatment. A displacement of the mandible frequently occurs upon changes in the occlusion guide paths due to fillings, crowns, interdental spaces, etc. The result of such a displacement may be a loss of the correct physiological position of the mandible and the jaw joints and, consequently, a loss of the physiological central occlusion position. The problem is particularly critical in the case of dorsal/ventral displacements and/or distraction/compression of the jaw joint associated with a unilateral or asymmetrical shift of the condyles. A displaced mandible can be returned into the correct physiological position by means of intervening in the occlusion. However, for such intervention to be successful with minimum patient discomfort, an exact diagnosis of the displacement of the mandible is necessary, i.e., in order to perform the corrective procedure it is necessary to know precisely how the position of the mandible is to be corrected.
Various techniques have been proposed, and in some cases implemented, for performing an occlusion analysis in order to determine the appropriate treatment for correcting a mandible displacement in a patient. One known method consists of articulating the maxilla in relation to the cranium and transferring the mandible by means of a function register. Another known method involves articulating either the mandible or maxilla and, in relation to the articulation, transferring of the opposing jaw by means of a function register.
Exemplary apparatus for performing a typical prior art occlusion analysis may be seen from German Patent No. 2,443,235. This German patent discloses a prior art articulator which includes mandibular and maxillary supports. The mandibular support includes a base plate with a block for the mandibular model and a pair of columns having spherical ends which define a horizontal articulator hinge axis. The maxillary support similarly includes a base plate with a block for the maxillary model. The maxillary support also has an outer arm which receives the spherical ends on the columns of the mandibular support whereby a swivel movement of the two supports relative to one another is permitted. The assembly of the jaw models in such a prior art articulator is usually carried out by first fixing the maxillary or mandibular model, in the form of a plaster cast, into the articulator in relation to the cranium or articulation, i.e., the model is placed in the spatial position relative to the articulator hinge axis which is identical to the hinge axis transferred from the patient. Thereafter, the opposing jaw model, also in the form of a plaster cast, is introduced into the articulator by means of a function register taken from the patient. The articulator allows the movements of the patient's jaws to be simulated and the occlusion to be assessed.
A significant disadvantage of prior art occlusion analysis apparatus and techniques, as briefly described above, resides in the necessity for use of a function register. The use of a function register requires the plotting of the centric relation in the patient and constitutes an important source of error. In general, the manual guiding of the mandible into the centric relation is necessary and is registered as the "instantaneous centric relation" using the centric register. The patient, however, can also be left to adopt the centric relation himself. The instantaneous centric relation can be affected by the defective configuration of the occlusal relief which may be present in the patient in which case a defective muscle reflex action is produced. Such a defective muscle reflex action makes it impossible for the patient to adopt the correct centric relation. Accordingly, the prior art techniques inherently cannot constitute a reliable measure for correct adjustment of the condyles and inaccurate diagnosis become unavoidable.